Ultrasonic surgical instruments are finding increasingly widespread applications in surgical procedures by virtue of the unique performance characteristics of such instruments. Depending upon the specific instrument configurations and operational parameters, ultrasonic surgical instruments can provide substantially simultaneous cutting of tissue and hemostasis by coagulation, potentially minimizing patient trauma. The cutting action is typically effected by an ultrasonic blade at the distal end of the instrument, with the blade transmitting ultrasonic energy to tissue brought into contact therewith. Ultrasonic instruments of this nature can be configured for open surgical use, or laparoscopic or endoscopic surgical procedures.
In one particular type of ultrasonic instrument, which may be described generally as a clamp coagulator, tissue is forced against an ultrasonic blade by a clamp arm which opposes at least a portion of the ultrasonic blade. In such instruments, the tissue which is positioned between the clamp arm and the blade is compressed against the blade as the clamp arm is closed. Thus the region of the ultrasonic blade opposing the closed clamp arm may be referred to as the compression zone. It is desirable in such an instrument to keep the speed of cutting and coagulation fast to reduce the heat generated in surrounding tissue. The speed at which tissue is cut and coagulated is a function of a number of parameters, including amplitude and frequency of the vibration of the blade and the pressure forcing the tissue against the blade. Instruments such as the clamp coagulator disclosed in U.S. Pat. No. 5,322,055 have blades that have a uniform cross-section in the compression zone. As a result of their uniform compression zone cross-section, the ultrasonic blades illustrated in U.S. Pat. No. 5,322,055 have vibration amplitudes that are greater at their distal ends than at their proximal ends. The result is that cutting and coagulation may take place faster at the distal end of the compression zone than at the proximal end, resulting either in a larger than desired area of coagulation at the distal end of the compression zone or a cut that is shorter and limited to an area near the distal end of the compression zone. Alternatively, tissue positioned at the distal end of the compression zone may be coagulated and cut before tissue at the proximal end is fully coagulated. While none of these limitations is detrimental to the patient, they may result in the surgeon taking smaller bites of the tissue to ensure full coagulation before cutting, thus slowing the surgeon down.
Previous ultrasonic instruments have included ultrasonic blades with variable cross-sectional areas, however, such instruments either do not vary the cross-sectional area of the blade in the compression region of a clamp coagulator. See, for example, U.S. Pat. No. 2,704,333 to Calosi et al. which illustrates an ultrasonic blade which decreases in cross-sectional area from the point of attachment to the distal end. The object of the Calosi invention is to increase vibrational amplitude of the distal end of the ultrasonic blade to effect work upon a piece at the distal end. Calosi teaches placing a higher concentration of mass at the distal end to increase the overall amplitude of the transmitting medium. U.S. Pat. No. 2,990,616, by Balamuth et al. illustrates an ultrasonic cutting tool that has differing geometries to drive vibrations of the tip to effect different characteristics on a cavity being cut into a workpiece. Two U.S. patents by Makool, U.S. Pat. No. 5,354,265 and U.S. Pat. No. 5,505,693, illustrate ultrasonic blades which decrease in cross-sectional area in a region proximal to the useful working area. Davidson et al., U.S., Pat. No. 5,322,055 illustrates ultrasonic blades with varying cross-sectional areas distal to the end of the clamp arm. The particular geometry is added to the tip of the blade so that it is available for useful tasks outside of the compression zone.
It would, therefore, be advantageous to design an ultrasonic clamp coagulator including an ultrasonic blade which has been specifically configured to increase the vibration amplitude in an area adjacent the proximal end of the clamp arm. It would, further, be advantageous to design an ultrasonic clamp coagulator instrument including an ultrasonic blade wherein the vibrational amplitude is greater at the proximal end of the compression zone than the vibrational amplitude in a conventional clamp coagulator. It would further be advantageous to design a clamp coagulator wherein the uniformity of cutting and coagulation within the compression zone is improved over the uniformity obtainable using conventional clamp coagulators.